Floyd Mayweather became the unified WBC and WBA welterweight champion but was given one of the toughest tests of his professional career in a majority decision victory over Marcos Maidana.

Mayweather was the overwhelming favourite to extend his unbeaten record to 46 wins from as many contests but came under some fierce pressure in the opening rounds from Maidana.

The Argentinian underdog came out swinging and caught Mayweather on a number of occasions although the pound-for-pound king gained the upper hand as the fight went on and finished strongly.

While one judge had the fight level at 114-114, the other two scores were 117-111 and 116-112 in Mayweather's favour.

Maidana, who suffered the fourth defeat of his 39-fight career, clearly felt he had done enough to have been given the nod and while he threw more punches, it was Mayweather's unerring accuracy that eventually saw him chalk up yet another win.

Such has been Mayweather's dominance, few gave Maidana any hope of springing an upset.

But he came charging out of the blocks and an early onslaught had Mayweather backing up in the opening round, while another furious flurry in the third once again gave Maidana the upper hand.

Mayweather appeared stunned by his opponent's start and although the American was cut for the first time in his career in the fourth round - albeit via a suspected unintentional headbutt - he gradually found his range.

Maidana kept coming forward, but while his wild swings often found fresh air, Mayweather has deadly accurate.

As the fight progressed, Mayweather started to target the body and a vicious punch to the abdomen left Maidana visibly reeling.

Neither fighter came close to forcing a stoppage, however, and Mayweather showed why he is held in such high regard with a commanding display in the championship rounds to seal victory.

While Amir Khan's superb victory over Luis Collazo earlier in the night appeared to put him on course for a clash with Mayweather, who is now three fights into a six-bout deal with US television network Showtime, the 37-year-old revealed Maidana's showing could force a re-match.

"This was a tough, competitive fight," he said afterwards.

"Normally when I fight I box and move. This was a tough fight. I wanted to fight.